Process for preparing thermoplastic elastomer

ABSTRACT

A THERMOPLASTIC ELASTOMER IS PREPARED BY HEATING BLOCK COPOLYMERS COMPRISING STYRENE, ACRYLONITRILE OR THEIR DERIVATIVES AS A THERMOPLASTIC COMPONENT, AND BUTADIENE, ISOPRENE, PHENYL BUTADIENE OR THEIR DERIVATIVES AS AN ELASTOMER COMPONENT IN THE PRESENCE OF A CROSS-LINKING AGENT SUCH AS BENZOYL PEROXIDE, IF NECESSARY, AT A TEMPERATURE OF 70* TO 130*C. FOR 2 TO 24 HOURS. THE THERMOPLASTIC ELASTOMER HAS A RUBBER ELASTICITY AND CAN BE READILY INJECTION MOLDED, AND IS VERY USEFUL AS ENGINEERING MATERIALS FOR SHOCK ADSORBERS AND MECHANICAL PARTS.

United States Patent C 3,819,766 PROCESS FOR PREPARING THERMOPLASTICELASTOMER Yasuo Hata and Yasusuke Shuto, Chibaken, Japan, assignors toIdemitsu Kosan Co., Ltd., Tokyo, Japan N Drawing. Filed Sept. 10, 1971,Ser. No. 179,590 Int. Cl. C08d 15/18, 15/22, 15/04, 19/08 US. Cl.260-879 1 'Claim ABSTRACT OF THE DISCLOSURE This invention relates to aprocess for preparing a thermoplastic elastomer, and more particularlyto a process for preparing a thermoplastic elastomer by heating blockcopolymers of styrene or acrylonitrile with butadiene or isoprene in thepresence of a cross-linking agent if required.

The present inventors have made vairous studies on a process forpreparing a thermoplastic elastomer, and as a result have found that anovel thermoplastic elastomer having excellent properties can beprepared by heating block copolymers comprising styrene or acrylonitrileas a thermoplastic component and butadiene or isoprene as an elastomercomponent in the presence of a crosslinking agent if necessary.

A polymerization catalyst used in the present invention is the so-calledliving polymerization catalysts, for example, alkali metals such aslithium, sodium and potassium, or alkyl compounds thereof.

A suitable solvent used in the polymerization is tertiary amines ormixtures thereof with tetrahydrofuran, ether, benzene, toluene, hexane,heptane, cyclohexane or the like. As the tertiary amines, aliphatictertiary amines such as trimethylamine, triethylamine, tripropylamine,etc. or heterocyclic amines such as pyridine, alkylpyridine, etc. areeffective in the present invention.

In carrying out the polymerization, a catalyst and a solvent are chargedinto a reactor at first, and then monomers are charged into the reactor.In that case, it is advantageous for several reasons to charge themonomers of the elastomer component initially. The polymers formed bypolymerization of the initially charged monomers are the so-calledliving polymers, whose activity is never lost unless there is an activecompound, for example, water, alcohol, carbon dioxide, or the like.Successively, other monomers are charged into the reactor to prepareblock copolymers.

Polymerization temperature is 50 to 150 C., and preferably to 50 C. fromthe view point of polymerization operation.

The thus obtained block copolymers are separated from the solvent, andthen subjected to heat treatment, whereby elastomer components of theblock copolymers are bonded to one another. The degree of bonding can beadjusted by controlling a heating temperature and heating time.

At that bonding, a net-like cross-linking can be carried out on thebasis of radical reaction by heating the block polymers in the presenceof a cross-linking agent such as benzoyl peroxide, tert.-butylhydroperoxide, acetyl per- 3,819,766 Patented June 25, 1974 oxide,di-tert.-butyl peroxide, azobisisobutyronitrile, etc. In that case, thedegree of bonding can be adjusted by controlling kind and concentrationof the cross-linking agent, heating temperature and heating time.

Other examples of the thermoplastic components used in the presentinvention than those as menitoned above include u-methylstyrene,methacrylonitrile, acrylic acid ester, methacrylic acid ester, etc. andother examples of the elastomer components used in the present inventionthan those as mentioned above include butadiene derivatives such asphenylbutadiene, etc.

The novel thermoplastic elastomer prepared according to the presentinvention has a rubber elasticity and can be readily injection-molded,and thus is very useful as engineering materials such as a shockabsorber, machine parts, etc.

Now, the present invention will be explained in detail, referring toExamples.

EXAMPLE 1 0.03 g. of metallic sodium in the form of a dispersion as acatalyst and 20 ml. of trimethylamine as a solvent were sampled into a100-m1. capacity, pressure-resistant glass reactor provided with astirrer, and 10 g. of styrene was added thereto and polymerized for onehour, while stirring the content of the reactor at 20 C. Then, 20 g. ofbutadiene was added thereto and subjected to polymerization for threehours. The resulting block copolymers were precipitated in methylalcohol and taken out. A portion of the block copolymers was dissolvedin an equal weight of benzene, and benzoyl peroxide was added thereto.The solution was heated at 80 C. for 2 hours. Another portion of theblock copolymers was dissolved in an equal weight of benzene, and thesolution was heated at 130 C. for 24 hours, without adding benzoylperoxide thereto. The thus heat treated block copolymers were separatedfrom benzene, and physical properties thereof were measured. The resultsare shown in Table 1, where the non-heat treated block copolymer isgiven for comparison.

EXAMPLE 2 0.05 g. of metallic sodium in the form of a dispersion as acatalyst and 50 ml. of a mixture solution of equal volumes oftetrahydrofuran and benzene as a solvent were sampled into a 300-ml.capacity, pressure-resistant glass reactor provided with a stirrer, andg. of butadiene was added thereto and polymerized for 5 hours, whilestirring the content of the reactor at 20 C. Then, 25 g. of styrene wasadded thereto and subjected to polymerization for two hours. Theresulting block copolymers were precipitated in methyl alcohol and takenout. A portion of the block copolymers was added to an equal weight ofbenzene and divided into three equal aliquots. Dilferent amounts ofbenzoyl peroxide were added to the first and the second aliquots whichwere then heated at C. for 12 hours. As for the third aliquot,azobisisobutyronitrile was added thereto, and the resulting solution washeated at 80 C. for 8 hours. The thus heat treated block copolymers wereseparated from benzene, and physical properties thereof were measured.The results are shown in Table 2, where the non-heat treated blockcopolymer is given for comparison.

TABLE 1 Modulus (kg/cm!) Amount of benzoyl peroxide Reduced Young's 100%200% 300% added (parts by weight per viscosity moduluselongaelongaelongapert by weight 01 copolymer) treatment [m /e](dyne/cmJ] tron tron tion None 0. 49 3. 92x10 2. 2 2. 2 2. 3 0... 1300., 24 hours- 0. 52 4. 21x10 2. 6 3. 2 3. 2 1/100 80 C., 2 hours 0. 849. 80X10 4. 2 4. 2 4. 2 2/100 do 0. 89 15. 0X10 7. 6 8. 8. 5

TABLE 2 Amount of benzoyl peroxide Modulus (kg/em!) (BPO) orazobisisobutyronitrile (AIBN) added (parts by Reduced Young's 100% 200%300% weight per part by weight Heat viscosity moduluselongaelongaelongaof copolymer treatment /c] [dyne/cmfi] tron tron tlonNone 0. 88 3. 33x10 3. 4 3. 4 3. 4 1/100 (BPOg. 80 0., 12 hours- 2.81x10 28. 7 38. 3 40. 3 2/100 (BPO do 4.26X10 43.5 56.7 66.1 1/100(AIBN) 70 C., 8 hour. 1. 40Xl0 14. 3 28.8 30.1

Gel was partially formed and exact measurement could not be effected.

EXAMPLE 3 thus heat treated block copolymers were separated frombenzene, and physical properties were measured. The re- 0.03 g. ofmetallic sodium in the form of a dispersion sults are shown in Table 4,where the non-heat treated as a catalyst and ml. of trimethylamine as asolvent block copolymer is given for comparison.

TABLE 3 Modulus (kg/cm!) Amount of benzoyl peroxide Reduced Young's 100%200% 300% added (parts by weight per Heat viscosity moduluselongaelongaelongapart by weight of copolymer) treatment [m /0.][dyno/cmfl] tion tion tion None 0.21 3.80Xl0 2.0 2.2 2.2 1/100 80 0., 2hours. 0.30 7. 00X10 3. 3 3. 4 3. 5

TABLE 4 Modulus (kg/cm!) Amount of benzoyl peroxide Reduced Young's 100%200% 300% added (parts by weight per eat viscosity moduluselongaelongaelongapart by weight of copolymer) treatment lflsp/c-l[dyne/cmJ] tlon tion tion 0--.- 0.35 3. 09X10 3. l5 3. 40 3. 55 1/101.11X10 11. 30 16. 30 17. 00

'Sparingly soluble in benzene, etc. Exact measurement could not beeffected.

were sampled into a IOO-ml. capacity, pressure-resistant glass reactorprovided with a stirrer, and 34 g. of butadiene was added thereto andpolymerized for 3 hours, while stirring the content of the reactor at 20C. Then, 6 g. of acrylonitrile was added thereto and subjected topolymerization for 2 hours. The resulting block copolymers wereprecipitated in methyl alcohol and taken out. Then, a portion of theblock copolymers was dissolved in an equal weight of benzene, andbenzoyl peroxide was added thereto. The solution was heated at 80 C. for2 hours. The thus heat treated block copolymers were separated frombenzene and physical properties thereof were measured. The results areshown in Table 3, where the non-heat treated block copolymer is givenfor comparison.

EXAMPLE 4 0.05 g. of metallic sodium in the form of a dispersion as acatalyst and 50 ml. of a mixture solution of equal volumes oftetrahydrofuran and benzene as a solvent EXAMPLE 5 0.05 g. of metallicsodium in the form of a dispersion 0 as a catalyst and 50 ml. of amixture solution of equal volumes of tetrahydrofuran and benzene as asolvent were sampled into a 300-ml. capacity, pressure-resistant glassreactor provided with a stirrer, and 70 g. of butadiene was addedthereto and polymerized for 5 hours, while stirring the content of thereactor at 20 C. Then, 15 g. of methyl methacrylate was added theretoand subjected to polymerization for 2 hours. The resulting blockcopolymers were precipitated in methyl alcohol and taken out. Then, aportion of the block copolymer was added to an equal weight of benzeneand benzoyl peroxide was added thereto. The solution was heated at 80 C.for 3 hours. The thus heat treated block copolymers were separated frombenzene, and physical properties were measured. The results are shown inTable 5, when the non-heat treated block copolymer is given forcomparison.

TABLE 5 Modulus (kg/cm!) Amount of benzoyl peroxide Reduced Youngs 100%200% 300% added (parts by weight per Heat viscosity moduluselongaelongaelongapart by weight of copolymer) treatment [m /e][dyne/cmJ] tion tion tlon 0 None 0. 4 3. 17x10" 3. 23 3. 31 3. 35 1/10080 0., 3 hours 1. 07x10 10.90 13.10 14.

sparingly soluble in benzene, etc. Exact measurement could not beeffected.

were sampled into a BOO-ml. capacity, pressure-resistant glass reactorprovided with a stirrer, and g. of butadiene was added thereto andpolymerized for 5 hours, while stirring the content of the reactor.Then, 15 g.

of acrylonitrile was added thereto and subjected to polym- 70 erizationfor two hours. The resulting block copolymers were precipitated inmethyl alcohol, and taken out. Then, a portion of the block polymers wasadded into an equal weight of benzene and benzoyl peroxide was addedthereto. The solution was heated at 80 C. for 3 hours. The

5 6 (c) heating the block copolymers produced by the 3,265,765 8/1966Holden et a1. 260-880RX foregoing steps at a temperature of 70 to 100 C.3,439,064 4/1969 Makowski et a1. 260879 for 2 to 5 hours and in thepresence of 1-2 wt. percent of benzoyl peroxide as a crosslinking agent.JOSEPH L. SCHOFER, Pnmary Exa-mmer References Cited 5 W. F. HAMROCK,Asslstant Exammer UNITED STATES PATENTS US. 01. X.R. 3,251,905 5/1966Zelinski 260879

